The gum around the wisdom tooth is inflammed. This is called pericoronitis. If its happening frequently then visit a nearby dentist and go for extraction of wisdom tooth.
Next Steps
Visit a nearby dentist as early as possible. Infection can spread to adjacent tooth as well as deep below inside bone. So you may need proper diagnosis and antibiotic.
Health Tips
Sometime the wisdom tooth get stucked and it won't erupt further. High chances of food getting stuck, cavity, sensitivity, infection, pain. So don't ignore. Visit your dentist to find out the reason and possible treatment options.